WIRE ROPE FAILURE

Wire can fail due to any number of causes. Here is a list of some of the common causes of wire rope failure.

Using the incorrect size, construction, or grade of wire rope;

Dragging rope over obstacles; Having improper lubrication; Operating over sheaves and drums of inadequate size;

Overriding or crosswinding on drums; Operating over sheaves and drums with improperly fitted grooves or broken flanges; Jumping off sheaves;

Subjecting it to acid fumes; Attaching fittings improperly; Promoting internal wear by allowing grit to penetrate between the strands; and

Subjecting it to severe or continuing overload.

Figure 4-7.-Correct and incorrect methods of measuring wire rope.

Figure 4-8.-Throwing a back turn to make wire lie down.

HANDLING AND CARE OF WIRE ROPE

To render safe, dependable service over a maximum period of time, wire rope must have the care and upkeep necessary to keep it in good condition. In this section, we'll discuss various ways of caring for and handling wire rope. Not only should you study these procedures carefully, you should also practice them on your job to help you do a better job now. In the long run, the life of the wire rope will be longer and more useful.

Coiling and Uncoiling

Once a new reel has been opened, it may be either coiled or faked down like line. The proper direction of coiling is counterclockwise for left-laid wire rope and clockwise for right-laid rope. Because of the general toughness and resilience of wire, however, it occasionally tends to resist being coiled down. When this occurs, it is useless to fight the wire by forcing down a stubborn turn; it will only spring up again. But if it is thrown in a back turn, as shown in figure 4-8, it will lie down properly. A wire rope, when faked down, will run right off like line; but when wound in a coil, it must always be unwound.

Wire rope tends to kink during uncoiling or unreeling, especially if it has been in service for a long time. A kink can cause a weak spot in the rope, which will wear out quicker than the rest of the rope. A good method for unreeling wire rope is to run a pipe or rod through the center and mount the reel on drum jacks or other supports so the reel is off the ground or deck (figure 4-9.) In this way, the reel will turn as the rope is unwound, and the rotation of the reel will help keep the rope straight. During unreeling, pull the rope straight forward, as shown in figure 4-9, and try to avoid hurrying the operation. As a safeguard against kinking, never unreel wire rope from a stationary reel.

To uncoil a small coil of wire rope, simply stand the coil on edge and roll it along the ground or deck like a wheel or hoop, as illustrated in figure 4-9. Never lay the coil flat on the deck or ground and uncoil it by pulling on the end because such practice can kink or twist the rope.

To rewind wire rope back onto a reel or a drum, you may have difficulty unless you remember that it tends to roll in the direction opposite the lay. For example, a right-laid wire rope tends to roll to the left.

Figure 4-9.-Unreeling wire rope (left) and uncoiling wire rope (right).

Figure 4-10.-Drum windings diagram for selecting the proper lay of rope.

Carefully study figure 4-10, which shows drum-winding diagrams selecting the proper lay of rope. When putting wire rope onto a drum, you should have no trouble if you know the methods of overwinding and underwinding shown in the illustration. When wire rope is run off one reel onto another, or onto a winch or drum, it should be run from top to top or from bottom to bottom, as shown in figure 4-11.

Kinks

If a wire rope should forma loop, never try to pull it out by putting strain on either part. As soon as a loop is noticed, uncross the ends by pushing them apart. (See steps 1 and 2 in figure 4-12.) This reverses the process that started the loop. Now, turn the bent portion over and place it on your knee or some firm object and push downward until the loop straightens out somewhat. (See step 3 in figure 4-12.) Then, lay the bent portion on a flat surface and pound it smooth with a wooden mallet. (See step 4 in figure 4-12.)

If a heavy strain has been put on a wire rope with a kink in it, the rope can no longer be trusted. Replace the wire rope altogether.

Figure 4-11.-Transferring wire from reel to drum.

Figure 4-12.-The correct way to takeout a loop in wire rope.

Lubrication

Used wire rope should be cleaned at frequent intervals to remove any accumulation of dirt, grit, rust, or other foreign matter. The frequency of cleaning depends on how much the rope is used. However, rope should always be well cleaned before lubrication. The rope can be cleaned by wire brushes, compressed air, or steam. Do not use oxygen in place of compressed air; it becomes very dangerous when it comes in contact with grease or oil. The purpose is to remove all old lubricant and foreign matter from the valleys between the strands and from the spaces between the outer wires. This gives newly applied lubricant ready entrance into the rope. Wire brushing affords a good opportunity to find any broken wires that may otherwise go unnoticed.

Wire rope is initially lubricated by the manufacturer, but this initial lubrication isn't permanent and periodic reapplications have to be made by the user. Each time a wire rope bends and straightens, the wires in the strands and the strands in the rope slide upon each other. To prevent the rope wearing out by this sliding action, a film of lubricant is needed between the surfaces in contact. The lubricant also helps prevent corrosion of the wires and deterioration of fiber centers. A rusty wire rope is a liability! With wire rope, the same as with any machine or piece of equipment, proper lubrication is essential to smooth, efficient performance.

The lubricant should be a good grade of lubricating oil, free from acids and corrosive substances. It must also be of a consistency that will penetrate to the center of the core, yet heavy enough to remain as a coating on the outer surfaces of the strands. Two good lubricants for this purpose are raw linseed oil and a medium graphite grease. Raw linseed oil dries and is not greasy to handle. Graphite grease is highly resistant to saltwater corrosion. Of course, other commercial lubricants may be obtained and used. One of the best is a semiplastic compound that is thinned by heating before being applied. It penetrates while hot, then cools to a plastic filler, preventing the entrance of water.

One method of applying the lubricant is by using a brush. In doing so, remember to apply the coating of fresh lubricant evenly and to work it in well. Another method involves passing the wire rope through a trough or box containing hot lubricant (figure 4-13). In this method, the heated lubricant is placed in the trough, and the rope passed over a sheave, through the lubricant, and under a second sheave. Hot oils or greases have very good penetrating qualities. Upon cooling, they have high adhesive and film strength around each wire.

As a safety precaution, always wipe off any excess when lubricating wire rope. This is especially important where heavy equipment is involved. Too much lubricant can get on brakes or clutches, causing them to fail. While in use, the motion of machinery

Figure 4-13.-Trough method of lubrication.

can throw excess oil onto crane cabs and catwalks, making them unsafe to work on.

Storage

Wire rope should not be stored in places where acid is or has been kept. The slightest trace of acid coming in contact with wire rope damages it at that particular spot. Many times, wire rope that has failed has been found to be acid damaged. The importance of keeping acid or acid fumes away from wire rope must be stressed to all hands.

It is especially important that wire rope be cleaned and lubricated properly before it is placed in storage. Fortunately, corrosion of wire rope during storage can be virtually eliminated if the lubricant film is applied properly beforehand and if adequate protection is provided from the weather. Bear in mind that rust, corrosion of wires, and deterioration of the fiber core greatly reduce the strength of wire rope. It is not possible to state exactly the loss of strength that results from these effects. It is certainly great enough to require close observance of those precautions prescribed for protection against such effects.

Inspection

Wire rope should be inspected at regular intervals, the same as fiber line. In determining the frequency of inspection, you need to carefully consider the amount of use of the rope and conditions under which it is used. During an inspection, the rope should be examined carefully for fishhooks, kinks, and worn, corroded spots. Usually, breaks in individual wires are concentrated in those portions of the rope that consistently run over the sheaves or bend onto the drum. Abrasion or reverse and sharp bends cause individual wires to break and bend back. The breaks are known as fishhooks. When wires are only slightly worn, but have broken off squarely and stick out all over the rope, the condition is usually caused by overloading or rough handling. Even if the breaks are confined to only one or two strands, the strength of the rope may be seriously reduced. When 4 percent of the total number of wires in the rope are found to have breaks within the length of one lay of the rope, the wire rope is unsafe.           Consider a rope unsafe when three broken wires are found in one strand of 6-by-7 rope, six broken wires in one strand of 6-by-19 rope, or nine broken wires in one strand of 6-by-37 rope.

Overloading a rope also causes its diameter to be reduced. Failure to lubricate the rope is another cause of reduced diameter since the fiber core will dry out and eventually collapse or shrink. The surrounding strands are thus deprived of support, and the rope's strength and dependability are correspondingly reduced. Rope that has its diameter reduced to less than 75 percent of its original diameter should be removed from service.

A wire rope should also be removed from service when an inspection reveals widespread corrosion and pitting of the wires.      Particular attention should be given to signs of corrosion and rust in the valleys or small spaces between the strands. Since such corrosion is usually the result of improper or infrequent lubrication, the internal wires of the rope are then subject to extreme friction and wear. This form of internal, and often invisible, destruction of the wire is one of the most frequent causes of unexpected and sudden failure of wire rope. The best safeguard, of course, is to keep the rope well lubricated and to handle and store it properly.

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